Microphone



Feb. 19, 1929 7 1,702,410

A. NYMAN MICROPHONE Filed March 1, 1924 2 Sheets-Sheet 1 INVENTORz4/exanaer Nyman.

ATTORNE Feb. 19, 1929. 1,702,410

A. NYMAN MICROPHONE Filed March 1924 2 Sheets-Sheet 2 C w L J WITNESSES:INVENTOR XV/dvf fl/exanaar /Vyma/7.

BY $.MW ATTORNEY support the microphone in such manner that provide ameans for clamping the diaphragm Patented Feb. 19, 1929.

UNITED STATES PATENT OFFICE.

ALEXANDER NYMAN, OF EAST ORANGE, NEW JERSEY, ASSIGNOE ELECTRIC &MANUFACTURING COMPANY, A CORPORATION OF TO wns'rmenousn PENNSYLVANIA.-

MICROPHONE.

Application filed March 1, 1924. Serial No. 696,177.

, mined path.

It is a further object of the invention to protect the microphone fromsuch damage as might be caused by rough handling.

It is a further object of this invention to provide a microphone ofmaterials which are non-resonant so that vibration of the materials outof which the microphone is constructed shall not produce undesiredresults.

It is a further object of this invention to use sonorous material forcertain parts of the instrument in order to reinforce the vibrations ofhigher frequency.

It is a further object of this invention to provide a microphonediaphragm as free as possible from tendency to vibrate at its ownnatural period. Incidentally, the invention includes an expedient bywhich non-conducting materials may be used in a microphone of the typein which electric currents are conducted by the diaphragm.

A further object of this invention is to prevent the cavities within themicrophone case from acting as resonators.

It is a further object of this invention to it shall receive no impulsesexcept those due to sound, all other mechanical jars being excluded.

It is a further objectof this invention to at its edges in such way thatnodistortion of the diaphragm, which might cause it to vibrate more atcertain periods than at others, shall be introduced by the clampingaction.

It is a further object of this invention to provide an electricalconnection to both faces of the diaphragm at the edge thereof withoutdefeating the object just stated.

Other objects of the invention and details of the construction will beapparent from the following description and accompanying drawings inwhich:

Figure 1 is a longitudinal sectional view of the diaphragm and itshousing,

Fig. 2 is a sectional view at right angles to Fig. 1, showing thediaphragm unit and a portion of the housing, other parts being omitted,

Fig. 3 is a diagrammatic view of the electrical connections,

Fig. 4 is radial sectional view through the clamping means and the edgeof the diaphragm,

Fig. is an elevational view of a modified supporting means, and

Fig. 6 is a rear view of the microphone of Fig. 5.

The microphone is supplied with a diaphragm 10 which consists of a disc11 of thin cardboard, upon each face of which is a strip 12 of goldleaf. Cardboard has been chosen because of its lack of tendency tomaintain vibrations after being distorted. This characteristic ofcardboard, in my opinion, is partly the result of internal frictionalforces developed when the diaphragm is distorted. Many other materialsmay be used, such as hard carbon, mica, celluloid, micarta andfullerboard, but cardboard gives the best results of the materials thatI have tested.

Most conveniently, these strips of gold leaf are made in one continuouspiece around the edges of the diaphragm, but two strips, one for eachface, may be used if desired. The gold leaf is secured to the cardboarddisc by an adhesive. An aqueous solution of the adhesive must not beused because the water would cause the cardboard disc to warp.Preferably, an alcoholic solution of shellac is employed.

In order to make electrical connection with the gold leaf on both facesof the cardboard, a conductor 13, best shown in Fig. 4, is provided,which extends around the edge of the diaphragm 11 into contact with thegold leaf on each face thereof. The con ductor 13 must be very small andflexible. Preferably, a very fine grade of braided conductor, such as isused in selector switches in automatic telephony, is employed, but asingle strand of ordinary telephone cord will serve well. At one end,the conductor 13 is soldered, or otherwise connected, to a terminalpiece 14 which is attached by a screw, or

by anyother desired fastening, to a hard rubber ring 15.

The ring 15 is one of a pair of rings 15 and 16 which surround thediaphragm 10. The

rings 15 and 16 are of hard rubber because that material iscomparatively free from ring. That is to say, it is non-sonorou's, inthat it does not produce a sustained note when struck. of the rings 15and 16 to vibrate and so set the diaphragm'into vibration at aparticular period is avoided. The rings are of slightly larger diameterthan the diaphragm in order that the edge of the diaphragm shall notengage the interior wall of the rings. Any possibility that the rings,by crowding the diaphragm, might cause it to buckle is thus avoided. Ifany distortion is introduced in the diaphragm, either by the ringscrowding it or by the clamping action described below being unevenlydistributed, there will result a tendency for the diaphragm to vibratemore readily at certain periods than at others and blasting orreinforcement of particular high notes will be caused.

The inner walls of the rings 15 and 16 have shoulders, to provide arecess, into which the diaphragm extends. Seated in this recess are softrubber washers 17. Preferably, there are two of these washers on oneside of the diaphragm and one on the other,

but any number of washers distributed in any desired way, may beemployed. There must, however, be, at least, one soft rubber washer oneach side of the diaphragm in order that it shall be cushioned on bothsides.

The washers are of flat sheet material. Soft rubber tubes or cords havebeen found to cause a tendency of the diaphragm to take an arched shapeand blasting results. Also, such members of circular cross sectionlosetheir effectiveness as the rubber ages. The combined thickness of thewashers and diaphragm should, when the washers are in their uncompressedcondition, slightly exceed the height of the recess.

are brought together, the pressure upon the diaphragm should be small.If the soft rubber washers are not of proper dimens ons, to

readily accomplish this, the combined thic'kness may be brought to thedesired size by introducing one or more washers of thin paper. The hardrubber rings are secured together by a plurality of screws 21, six beingshown by way of example, in Fig". 2. A small-er number isdisadvantageous because it is difficult to distribute the pressure withsuflicient uniformityunless the number of screws be large. A greaternumber than six may be used, if desired. By suitably adjusting each ofthe screws 21, the pressure of the washers 17 against the diaphragm maybe made uni form throughout the whole circumference.

The conductor 13 is so small that the extra For this reason, anytendency This excess should only be slight because, when the rings 15and 16 compression of the washers caused by it is not sufficient toproduce any perceptible difference in the distribution of the pressureupon the diaphragm. The flat shape of each strand in a cable-,or of thesingle strand, if a single one be used, is an additional reason why noappreciable excess of pressure upon the washers and diaphragm is causedby the wire.

A cup 22, preferably of brass, holds a body 23 of carbon granules. Theedge of this cup is faced with a felt washer 24 which contacts with thediaphragm. The contact is suflicient-ly close to prevent the escape ofthe carbon granules 23. At the same time, it is sufficiently lighttopermit vibration of the diaphragm 10. During such vibration, however,the diaphragm compresses the felt slightly. Since the felt is morereadily compressed than the body of carbon granules, the magnitude ofpressure changes in that body caused by the motion of the diaphragm isnot diminished by the presence of the felt. The felt, however, assistsin damping out vibrations, consequently, if there be any tend ency ofthe diaphragm to vibrate at its own natural period, it is diminished bythe felt.

The bottom of the cup 22 is covered by a disc 25 of metal having afacing of carbon soldered thereto. This disc is secured in place by ascrew 26 integral therewith and extending through the bottom of the cup.The screw is received in a cylindrical holder 27 by means of which thecup is secured in position in a hub 28. A slot 29, suitable for thereception of a screw-driver, facilitates adjustment of the position ofthe cup.

By giving the holder 27 a rotary movement with a screw driver, theposition of the holder in the hub may be adjusted lengthwise withgreater nicety than no rotation of the holder were possible. The slot 29is also a convenienc'e when the cup 22, false bottom 25 and holder 27are being assembled. A set screw 31, through the wall of hub 28, serves"to hold the cup in position.-

The hub 28 is supported upon a bridge 32 which extends diametricallyacross the ring 16 and is secured thereto at each end by screws 33. Thisbridge is made of brass. Bridges of hard rubber have been tried but theadvantage gained thereby is very slight. Moreover, it is quite possiblethat the ringing or resounding quality of the brass reinforcesvibrations at certain very high pitches, at which such reinforcement isdesirable. A

terminal screw 34 mounted upon the bridge similar bridge 42 is mounted,which carries a cup 43 holding a body 45 ofca'rbon granules.

The cup 43 is of slightly greater diameter than the cup 22 so that thefelt washer 44 upon the cup 43 contacts with the diaphragm over anannular area just outside of that contacted by the felt washer Theconductor 46 is secured to the bridge 42 in a way similar to that usedto secure the conductor 35 to the bridge 32 and it also extends to theoutside of the instrument. A third conductor 50 extends from the outsideof the'instrument to the terminal 14 secured on the ring 15.

The ring 16 is provided with a bead 51 which serves as an abutment for acover 52 extending over the front of the microphone.

' The central part of this cover is open and, to

protect the instrument, the opening is occupied by an arched screen 53.

Between the screen 53 and the diaphragm 10 is a space which, if notmodified, could act like a short organ pipe and thus provide resonancefor certain high-pitched sounds. This action would result in suificientblasting to seriously interfere with the reproduction of music. To avoidthis difliculty, the cylindrical wall of the cover has a felt lining 54.The action of this lining, by absorbing sound energy, prevents the spacebetween the screen 53 and the diaphragm from acting as a resonator.

The rear of the microphone is closed by a cover 55 of any convenientshape. The bead 51 acts as a stop for this cover also. An opening 56 isprovided in this cover, through which the conductors 35, 46 and 50emerge.

The microphone unit, the cover enclosing it and the conductors, arehoused within an enclosure comprising a tube 60 of any convenientmaterial. Micarta has been found to serve well. At the rear, theenclosure includes a disc 61, also of micarta, although many othermaterials will serve. A reinforcing strip 62 is provided at that part ofthe sleeve 60 where the conductors 35, 46 and 50 emerge and bindingposts 63, 64 and 65, one for each conductor, are mounted on thereinforcing strip.

The space between the micarta enclosure and the microphone casing isfilled with felt. The felt used is sufficiently hard to support themicrophone in place within the enclosure and protects it from injury byrough handling. It is sufficiently loose in its texture to afford adamping action upon all sounds except those of very low pitch. Theinterstices between the fibres of felt are small enough so that none ofthem can constitute a resonance chamber for sound vibrations, the pitchof which is within the limit of audition. Care must be taken in cuttingand fitting the various pieces of felt, that no cavities are left whichcan form such resonance chambers. The damping action of the feltassists, however, in preventing resonance in such cavities as arepresent.

The front layer 67 of felt is a ring surrounding the screen 53. Theopening 68 in this ring constitutes a channel through which sound canreach the microphone. The layers of felt immediately at the rear of themicrophone are so cut as to provide a channel through which theconductors 35, 46 and 50 may reach the binding posts 63, 64 and 65.

In order to support the instrument, two bands 70 of metal are placedaround the two ends of the sleeve and each band is secured by a bolt 71.One end of each band is made to project upward beyond the bolt and has ahole 72. The holes serve as attaching means for strips 73, of extensiblerubber or other flexible material which form a suspensory device. Theupper ends of the rubber strips are secured to any desired support. Ithas been found that helical springs or other metal suspensory devices donot serve well for hanging the microphone, because they possess aresounding quality and produce a ring which gives rise to a noticeableblast.

The microphone. is connected to the radio sending apparatus by means ofthe circuit illustrated in Fig. 3, in which the battery feeds thepotentiometer 7 6. One end of this potentiometer is connected to theterminal 14 and thereby to the gold leaf upon the diaphragm. The otherside of the potentiometer is connected to the middle point of aninductor 77, which forms the primary winding of a transformer, thesecondary winding 78 of which is connected to the amplifier or othersuitable element of the radio system. The two terminals of the inductor77 are connected to the two cups 22 and 43 by means of the conductors 35and 46, the bridges 32 and 42 and the cup holders. In shunt to theinductor 77 is an adjustable resistor 79 of greater resistance than themicrophone. This resistor serves to give added steadiness to the signalstransmitted.

The microphone when associated with the enclosure described, isparticularly suitable for transmitting music. lVhen speech is to betransmitted it is desirable to use, instead of the rear cover 55, a rearcover provided with a screen 81 (Fig. 6) similar to the screen 53 exceptthat it has an opening for the conductors.

Obviously, such a microphone cannot be used in the enclosure 60, becausethe opening at the rear thereof would be useless. It is, therefore,mounted in a ring 82 supported on a standard 83 similar to the usualdesk-telephone stand. The ring 82 is provided wit-h a number of hooks 84through each of which extends a rubber suspensory device 85. This devicemay consist of one or more extensible rubber bands for each hook, or asingle extensible rubber band may be used, passing through all of thehooks. The microphone is supplied with a number of projecting attachmentdevices 86, preferably fastened to the microphone by putting screws intoholes 87 T in the bead 51. The suspensory device-85-is'made to passaround each of the projections'86 and so holds the microphone in placeWithin the ring. The conductors 35, 4:6 and 50eX- tend from themicrophone into the interior of the standard 83 and out at the base-88in the same Way as an ordinary telephone cord.

When the user speaks into the microphone shown in Fig.5, there is noreflection of his voice from the rear of the casing or of the enclosurebecause both of these have open rear faces. Consequently, resonance dueto the space between the diaphragmiand the rear face is avoided. Theenclosure and support illustrated in Fig. l afford protection fromextraneous noisesand a selective reception of very low tones. Theseproperties are of great advantage when transmitting music but are not soimportant when transmitting speech.

Although I have illustrated and specifically described but one form onmy microphone I unit and but two'forms of enclosure and supporttherefor, many variations in the details of the structure Will beobvious to those skilled in the art and I do not intend the specificdisclosure made to be considered as a limitation.

I claim as my invention:

1. In a microphone, a body of loose grains of carbon, :a cup forholdingsaid body, a felt rim secured to said cup and surrounding themouth thereof, a diaphragm engaging said rim, and means for adjustingthe cup toward and from the diaphragm to regulate the damping action ofsaid felt rim.

2. In a microphone, a diaphragm, two granule cups, one on each sidethereof concentric therewith and of different diameters and dampingmeans coextensive with the cups.

3. In a microphone, a diaphragm, -tWo granule cups, one on each sidethereof con centric therewith and of diiferent diameters, damping meanson the edge of each cup, the outeredge of the smaller damping meansbeing approximately opposite the inner edge of the large damping means.

4. In a microphone, a diaphragm, annular dampin means contacting thediaphragm on each face, one of said means being of larger dia neter thanthe other.

5. A diaphragm for microphones comprising a plate of cardboard having acoating of gold foil secured to each face thereof by nonaqueousadhesive.

6. In a sound-responsive device, a microphone unit, a casing housingsaid unit and having a sounda'eceptive opening, an enclosure surroundingsaid casing and having an opening in alignment with said soundreceptiveopening, a packing of material which prevents the passage ofhigh-pitched sounds, said packing filling said enclosure externalof saidcasing, and an opening through said packing, extending from said openingin the enclosure to said sound receptive opening.

In testimony whereof, I have hereunto sub scribed my name this 18th dayof February,

ALEXANDER NYMAN.

